1. Field of the Invention
The present invention relates generally to heating systems, and more particularly to catalytic heating systems that generate heat and electricity via an oxidation reaction within a cavity having porous catalytic walls.
2. Description of the Related Art
The early inventions of liquid fueled heating systems include the oil lamp and the candle. Each early liquid fueled heating system wicks fuel up to a region where the fuel could evaporate and combust. Oils and kerosene lanterns can use the wick directly. Alcohol burners, and in particular methanol burners, need an added thermal conductor and sleeve tube to the wick in order to deliver enough heat to pre-heat the fuel and channel vaporized fuel to the burn zone. Without such thermal conductor and sleeve tube around the alcohol burners, the fuel, the flame front, or plasma burns the associated wick.
Recently a need to cleanly burn alcohols rather than other hydrocarbons such as, for example, oils and kerosene, has arisen. Such alcohols can be derived from waste materials, also known as “biomass,” or manufactured from “alternative energy” sources.
There are several advantages for burning alcohols rather than hydrocarbons. For example, methanol burns without, smoke, soot and odors. Alcohol fuels, in contrast to kerosene, burn cooler and can be extinguished with water. Methanol and the alcohols will self start catalytic combustion on suitable catalysts and produce substantially complete combustion. Catalytic hydrocarbon burners, on the other hand, generally require a preheating step for the catalyst. Such advantages in burning alcohols, rather than hydrocarbons, allow for low cost and fuel effective heaters.
In view of the forgoing, the various exemplary embodiments of the present invention achieve an efficient combustion heater and heat transfer for space heating. Other various and similar applications could arise out of the exemplary embodiments of the present invention as well.
The mechanism of diffusing fuel and air from separate routes into the fuel, rather than mixing the air and fuel together and then arriving at the catalyst, results in a significantly improved combustion situation.
Conventional burners that mix fuel and air together for combustion within a cavity can lead to unsteady and explosive burns of the fuel and air. Typically, the larger the cavity of the conventional burner, the larger the associated explosion. This can lead to burner fatigue and disastrous results such as, for example, rupture of the heater.
It has been found that fuel air mixtures can vary in time which may lead to flame front loss and explosions when re-establishing the flame. This is a particular problem in burning of tail gasses from refineries or catalytic reaction systems of two streams of reactants.
To avoid such possible disasters, in various exemplary embodiments of the present invention, fuel and air are separated by a porous catalytic bed. The fuel and air inter-diffuse to each other through the porous catalytic bed, and ideally there is no significant non-catalytic cavity filled with an air fuel mixture.
In the present invention, it has surprisingly been found there is a reduced cost and operational advantage to having a cavity within the porous catalyst bed, and that plasma forms within such cavity. The inter-diffusion of fuel and air through the porous catalytic bed achieves a high occupation time over the catalyst for molecules that is equal for all molecules present rather than the situation in forced flow through catalytic beds. In the latter, laminar flow, also known as “streamline flow” or “non-diffusionally driven,” mass flow through a random porous catalytic bed leads to non-uniformity of gas composition radially in the flow channels, and an uneven flow distribution such that larger channel flows dominate throughput, and flow rates therein can be high enough to prevent sufficient diffusion to the catalytic sites to catalytically react a portion of the fuel and air. Thus, some of the fuel air mixture can pass by the catalytic surfaces without interacting and produce incomplete combustion. Within the catalytic bed the inter-diffusion catalytic combustion can achieve a temperature gradient from highest on the interior cavity and then drops to the outside, important to achieving complete combustion. The present invention has found that if the outer surfaces of the catalytic bed are kept below 400° C. to 200° C. centigrade with a stoichiometric excess of oxygen to methanol fuel, and a rock wool/catalytic bed is uniformly catalytically active the unburned combustion products can drop below 1 part in 10,000 or the limits of our measuring equipment. By depending on this process of inter-diffusion through a separating catalytic bed wall, the new heater invention does not require fans or pumps. The new invention may use convection air flow and/or jets to admit fuel vapor or air in a distributed fashion, leading to a simple, quiet, clean burning and robust heater system. The hot catalytic surfaces which face the air flow also can fully oxidize and thereby eliminate gases in the air stream such as hydrocarbons and carbon monoxide as they flows through the heater. Additional devices that can be coupled with the heater air inlet are air filters, electrostatic air filters, photo catalytic air filters, absorbers, adsorbers, scrubbers, similar devices or, for the exhaust air, water condensers and/or carbon dioxide traps. Scents and perfume emitters arranged with the heater could be used, and some high molecular weight examples may pass through the heater unoxidized and so may be borne as an additive to the fuel. This heater system can also be used in conjunction with a membrane catalytic heater pending U.S. patent application Ser. No. 10/492,018, incorporated by reference.